Mathilde de Morny (26 May 1863 – 29 June 1944) was a French noblewoman and artist.
She was also known by the nickname "Missy" or her pseudonym as an artist, "Yssim" (an anagram of Missy), "Max", "Uncle Max" (French: Oncle Max) and "Monsieur le Marquis".
Active as a sculptor and painter, she studied under Comte Saint-Cène and the sculptor Édouard-Gustave-Louis Millet de Marcilly.